Fault-current protection device with an overload protection device

Abstract

A residual current device ( 1 ), having a residual current tripping circuit ( 4 ) which is independent of the mains voltage and contains a core balance transformer ( 2 ), and having overload protection ( 18 ) arranged in an overload tripping circuit ( 10 ) which is supplied with the mains current, wherein the residual current tripping circuit ( 4 ) and the overload tripping circuit ( 10 ) contain a common tripping relay ( 7 ) for operating a switching mechanism ( 8 ) which switches a conductor network (LN).

What is claimed is:  
     
       1. A residual current device, comprising: 
       a residual current tripping circuit which is independent of the main voltage and includes a core balance transformer;  
       an overload tripping circuit which is supplied with the main current, wherein the residual current tripping circuit and the overload tripping circuit include a common tripping relay for operating a switching mechanism which switches a conductor network; and  
       a power supply unit connected upstream of the overload tripping circuit and connected via a respective supply line to each conductor of the conductor network, the power supply unit being designed with a high impedance such that each supply line has a resistance of at least about 2.5 kΩ/V-times the magnitude of the main voltage in volts.  
     
     
       2. The residual current device as claimed in  claim 1 , wherein the overload tripping circuit comprises an evaluation circuit, which is connected to a temperature sensor. and is upstream of a threshold value circuit, for determining a load state. 
     
     
       3. The residual current device as claimed in  claim 2 , wherein the temperature sensor is arranged in the region of the core balance transformer. 
     
     
       4. The residual current device as claimed in  claim 2 , wherein the temperature sensor is a temperature-dependent non-reactive resistor. 
     
     
       5. The residual current device as claimed in  claim 1 , wherein the power supply unit includes a capacitor for storing the energy required to operate the tripping relay. 
     
     
       6. The residual current device as claimed in  claim 5 , wherein the overload tripping circuit is designed with a high impedance such that the current draw of the overload tripping circuit has an upper limit of about 80-90% of the quotient of 1/{square root over (3)}-times the main voltage and twice the resistance in each supply line where the current draw of the overload tripping circuit is less than or equal to F times the main voltage and F is a number between 0.8 and 0.9. 
     
     
       7. The residual current device as claimed in  claim 1 , wherein the power supply unit includes a capacitor for storing the energy required to operate the tripping relay. 
     
     
       8. The residual current device as claimed in  claim 7 , wherein the overload tripping circuit (I) is designed with a high impedance such that the current draw of the overload tripping circuit has an upper limit of about 80-90% of the quotient of 1/{square root over (3)}-times the mains voltage (U 1 /{square root over (3)}) and twice the resistance in each supply line where I≦(F*U 1 /{square root over (3)})/(2*R) and F is a number between 0.8 and 0.9.